Imaging alkane layers at the liquid/graphite interface with the scanning tunneling microscope

McGonigal, G. C.; Bernhardt, Rita; Thomson, D. J.

doi:10.1063/1.104234

Cited by 420 publications

(301 citation statements)

References 11 publications

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“…A set of n-alkanes (C N H 2Nϩ2 , Nϭ5, 6,7,8,10,12,14,16,18,20,22,24,26,44, 60͒ were purchased having purities of Ͼ98% from Aldrich Chemicals. Acros Chemicals supplied n-alkanes (Nϭ28, 32, 36, 40͒ in purities of Ͼ97%.…”

Section: Methodsmentioning

confidence: 99%

Effects of conformational isomerism on the desorption kinetics of n-alkanes from graphite

Paserba

Gellman

2001

The Journal of Chemical Physics

140

176

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The dynamics of oligomer desorption from surfaces have been studied by measuring the desorption kinetics of a set of n-alkanes from the surface of single crystalline graphite. Desorption rates were measured using a set of 21 monodispersed n-alkanes (C N H 2Nϩ2 ,5рNр60) each adsorbed at coverages in the range Ͻ0.1 to Ͼ1 monolayers. Desorption is observed to be a first-order process with a desorption barrier (⌬E des ‡ ) that is independent of coverage. The pre-exponential of the desorption rate constant is independent of the oligomer chain length and has a value of ϭ10 19.6Ϯ0.5 s Ϫ1 . We also find that ⌬E des ‡ has a nonlinear dependence on chain length and takes the empirical form ⌬E des ‡ ϭaϩbN ␥ , with the exponent having a value of ␥ϭ0.50Ϯ0.01. More interestingly, we have proposed a mechanism for the desorption process and a model for the energetics and the entropy of the oligomers on the surface that provide an extremely good quantitative fit to the observed chain length dependence of ⌬E des ‡ . ⌬E des ‡ is given by the difference in energy between the gas phase n-alkane and the conformation of the adsorbed n-alkane with the minimum free energy at the desorption temperature. These results reveal that conformational isomerism plays a significant role in determining the desorption kinetics of oligomers from surfaces.

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Section: Methodsmentioning

confidence: 99%

Effects of conformational isomerism on the desorption kinetics of n-alkanes from graphite

Paserba

Gellman

2001

The Journal of Chemical Physics

140

176

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“…In addition, the physisorption of alkanes has been studied on Au(111), 6 Pt(111), 7,8 Pt(110), 9 Ir(110), 10 Cu(100), 11 Ru(001), 12 and Cu(111), 13 under UHV conditions. However, the local arrangement of the alkanes on a metal surface has not been investigated in contrast to numerous reports of alkane adlayers on graphite at the solid/liquid interface, [14][15][16][17][18][19][20][21] although studies using molecular dynamics 12,[22][23][24][25][26][27] and infrared spectroscopy [28][29][30][31][32] under UHV conditions have been carried out after the reports by Firment and Somorjai. Furthermore, the structure of the alkane/metal interface in solution was not investigated.…”

Section: Introductionmentioning

confidence: 99%

Two-Dimensional Crystals of Alkanes Formed on Au(111) Surface in Neat Liquid: Structural Investigation by Scanning Tunneling Microscopy

Yamada

Uosaki

2000

J. Phys. Chem. B

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In situ scanning tunneling microscopy revealed the formation of the two-dimensional (2D) crystals of n-alkanes (C n H 2n+2 , n ) 12-17) on a Au(111) surface in neat liquid at room temperature. The molecules were adsorbed on the gold surface with their molecular axis parallel to the surface plane. The molecular rows of even-and odd-numbered alkanes ran in the nearest-neighbor (NN) atomic direction and the next-nearest-neighbor atomic direction of the gold surface, respectively. The molecular axis was oriented close to the NN direction of the gold surface in both odd-and even-numbered alkanes. Although there are two NN directions with respect to the direction of the bridging row of the herringbone structure due to the reconstruction of the Au(111) surface with crossing angles of 30°and 90°, the molecular axis was preferentially oriented in the NN direction with a crossing angle of 30°. The 2D crystal of alkanes was not formed on the iodine-modified Au(111) surface, confirming that the molecule-substrate interaction played an important role in forming the 2D crystal of alkanes.

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“…3,24,25 Of these systems, probably the best characterized are monolayers of C32 and C24 on high-quality graphite basal-plane surfaces that have been investigated by scanning tunneling microscopy ͑STM͒, [10][11][12][13][14] x-ray diffraction, 15 and neutron scattering. [16][17][18][19][20][21] Graphite substrates also have the advantage that relatively reliable empirical atom-atom potentials are available for representing the molecule/graphite basal-plane interaction.…”

Section: Introductionmentioning

confidence: 99%

“…Previous experimental studies of the monolayer structure of intermediate-length alkanes have focused on high-quality solid surfaces of graphite, [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] Ag͑111͒, 22,23 and SiO 2 . 3,24,25 Of these systems, probably the best characterized are monolayers of C32 and C24 on high-quality graphite basal-plane surfaces that have been investigated by scanning tunneling microscopy ͑STM͒, [10][11][12][13][14] x-ray diffraction, 15 and neutron scattering.…”

Section: Introductionmentioning

confidence: 99%

Structure and phase transitions of monolayers of intermediate-length n-alkanes on graphite studied by neutron diffraction and molecular dynamics simulation

Diama

Matthies

Herwig

et al. 2009

The Journal of Chemical Physics

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We present evidence from neutron diffraction measurements and molecular dynamics ͑MD͒ simulations of three different monolayer phases of the intermediate-length alkanes tetracosane ͑n-C 24 H 50 denoted as C24͒ and dotriacontane ͑n-C 32 H 66 denoted as C32͒ adsorbed on a graphite basal-plane surface. Our measurements indicate that the two monolayer films differ principally in the transition temperatures between phases. At the lowest temperatures, both C24 and C32 form a crystalline monolayer phase with a rectangular-centered ͑RC͒ structure. The two sublattices of the RC structure each consists of parallel rows of molecules in their all-trans conformation aligned with their long axis parallel to the surface and forming so-called lamellas of width approximately equal to the all-trans length of the molecule. The RC structure is uniaxially commensurate with the graphite surface in its ͓110͔ direction such that the distance between molecular rows in a lamella is 4.26 Å = ͱ 3a g , where a g = 2.46 Å is the lattice constant of the graphite basal plane. Molecules in adjacent rows of a lamella alternate in orientation between the carbon skeletal plane being parallel and perpendicular to the graphite surface. Upon heating, the crystalline monolayers transform to a "smectic" phase in which the inter-row spacing within a lamella expands by ϳ10% and the molecules are predominantly oriented with the carbon skeletal plane parallel to the graphite surface. In the smectic phase, the MD simulations show evidence of broadening of the lamella boundaries as a result of molecules diffusing parallel to their long axis. At still higher temperatures, they indicate that the introduction of gauche defects into the alkane chains drives a melting transition to a monolayer fluid phase as reported previously.

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Imaging alkane layers at the liquid/graphite interface with the scanning tunneling microscope

Cited by 420 publications

References 11 publications

Effects of conformational isomerism on the desorption kinetics of n-alkanes from graphite

Effects of conformational isomerism on the desorption kinetics of n-alkanes from graphite

Two-Dimensional Crystals of Alkanes Formed on Au(111) Surface in Neat Liquid: Structural Investigation by Scanning Tunneling Microscopy

Structure and phase transitions of monolayers of intermediate-length n-alkanes on graphite studied by neutron diffraction and molecular dynamics simulation

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